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Ultrathin ZnO nanostructures present interesting two-dimensional (2D) graphene-like structure in contrast to wurtzite structure in bulk ZnO. Growth on Au(111) has been regarded as a well-established route to the 2D ZnO layers while controlled growth of uniform ZnO nanostructures remains as a challenge. Here, reactive deposition of Zn in O3 and NO2 was employed, which is investigated by scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS). We demonstrate that uniform ZnO monolayer nanoislands and films can be obtained on Au(111) using O3 and uniform ZnO bilayer nanoislands and films form on Au(111) using NO2, respectively. Formation of atomic oxygen overlayers on Au(111) via exposure to O3 is critical to the formation of uniform ZnO monolayer nanostructures atop. Near ambient pressure XPS studies revealed that nearly full hydroxylation occurs on monolayer ZnO structures upon exposure to near ambient pressure water vapor or atomic hydrogen species, while partial surface hydroxylation happens on bilayer ZnO under the same gaseous exposure conditions.
This work was financially supported by the National Natural Science Foundation of China (Nos. 21825203, 91545204, 21688102, and 21621063), the National Key Research and Development Program of China (Nos. 2016YFA0200200 and 2017YFB0602205), and Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB17020000). The authors thank the support for Nano-X from Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO). The fruitful discussion with Yuemin Wang in Karlsruhe Institute of Technology (KIT) is highly appreciated.